U.S. patent number 10,758,753 [Application Number 15/764,206] was granted by the patent office on 2020-09-01 for ducting system.
This patent grant is currently assigned to Commonwealth Scientific and Industrial Research Organisation. The grantee listed for this patent is Commonwealth Scientific and Industrial Research Organisation. Invention is credited to Hua Guo, Shi Su, Xinxiang Yu.
United States Patent |
10,758,753 |
Su , et al. |
September 1, 2020 |
Ducting system
Abstract
The present invention relates to a ducting system (100) for
conveying a flow of a gaseous feed (110) comprising a combustible
component from an inlet to at least one combustion module (12), the
ducting system (100) utilising a combination of a sensor (C0) for
measuring the concentration of the combustible component in the
gaseous feed (110), a flame detector (F0, F1, F2, F3, . . . , Fn) a
shut-off valve (6) and a flame arrestor (5) located in a flow path
of the gaseous feed upstream of the shut-off valve (6) such that a
measurement of a concentration of combustible material in the
gaseous feed over a specified concentration by the sensor (CO)
causes the shut-off valve (6) to be configured to the closed
position for preventing flow of a gaseous feed comprising a
combustible mixture of the combustible component from reaching an
ignition source and/or detection of flame by the flame detector
(F0, F1, F2, F3, . . . , Fn) causes shut-off valve (6) to be
configured to the closed position for attenuating propagation of a
flame towards the inlet.
Inventors: |
Su; Shi (Pullenvale,
AU), Guo; Hua (Pullenvale, AU), Yu;
Xinxiang (Pullenvale, AU) |
Applicant: |
Name |
City |
State |
Country |
Type |
Commonwealth Scientific and Industrial Research
Organisation |
Acton, Australian Capital Territory |
N/A |
AU |
|
|
Assignee: |
Commonwealth Scientific and
Industrial Research Organisation (Action, Australian Capital
Territory, AU)
|
Family
ID: |
58629622 |
Appl.
No.: |
15/764,206 |
Filed: |
October 27, 2016 |
PCT
Filed: |
October 27, 2016 |
PCT No.: |
PCT/AU2016/051008 |
371(c)(1),(2),(4) Date: |
March 28, 2018 |
PCT
Pub. No.: |
WO2017/070737 |
PCT
Pub. Date: |
May 04, 2017 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20180272165 A1 |
Sep 27, 2018 |
|
Foreign Application Priority Data
|
|
|
|
|
Oct 30, 2015 [AU] |
|
|
2015904458 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A62C
3/06 (20130101); E21F 1/00 (20130101); A62C
4/02 (20130101); E21F 7/00 (20130101); F23N
5/24 (20130101); F23G 7/06 (20130101); F23G
2209/141 (20130101); F23G 2208/10 (20130101); F23G
2204/103 (20130101); F23N 2231/28 (20200101) |
Current International
Class: |
A62C
3/06 (20060101); E21F 1/00 (20060101); F23G
7/06 (20060101); E21F 7/00 (20060101); A62C
4/02 (20060101); F23N 5/24 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
101589271 |
|
Jan 2012 |
|
CN |
|
202876161 |
|
Apr 2013 |
|
CN |
|
202914127 |
|
May 2013 |
|
CN |
|
204201939 |
|
Mar 2015 |
|
CN |
|
204201939 |
|
Mar 2015 |
|
CN |
|
204457839 |
|
Jul 2015 |
|
CN |
|
2825286 |
|
Jan 2015 |
|
EP |
|
PCT/AU2009/001708 |
|
Dec 2009 |
|
WO |
|
Other References
International Search Report and Written Opinion corresponding to
PCT/AU2016/051008, dated Dec. 21, 2016, nine pages. cited by
applicant .
First Office Action for Chinese Application No. 201680062706.8
dated Mar. 4, 2020, all pages. cited by applicant.
|
Primary Examiner: Zhou; Qingzhang
Attorney, Agent or Firm: Kilpatrick Townsend & Stockton
LLP
Claims
The invention claimed is:
1. A ducting system for conveying a flow of a gaseous feed of
ventilation air derived from a coal mine comprising a combustible
component from an inlet to at least one combustion module, the
system comprising: a shut-off valve configurable to have an open
position to allow the flow of the gaseous feed from the inlet to
the at least one combustion module and a closed position to prevent
the flow of the gaseous feed from the inlet to the at least one
combustion module; a sensor to measure a concentration of the
combustible component in the flow of the gaseous feed, the sensor
located upstream of the shut-off valve; a flame detector located
downstream of the shut-off valve; a flame arrestor located in a
flow path of the gaseous feed upstream of the shut-off valve; and a
source of fire retardant and a fire retardant valve feeding one or
more fire retardant injection points for controlling flow of the
fire retardant into the ducting system, the one or more fire
retardant injection points positioned between the flame arrestor
and the at least one combustion module, wherein the shut-oft valve
is operatively associated with the sensor such that a measurement
of a concentration of the combustible component in flow of the
gaseous feed over a specified concentration by the sensor causes
the shut-off valve to be configured to the closed position for
preventing flow of a gaseous feed comprising a combustible mixture
of the combustible component from reaching an ignition source,
wherein the specified concentration is 1.25% methane as the
combustible component wherein the shut-off valve is operatively
associated with the flame detector such that detection of flame by
the flame detector causes the shut-off valve to be configured to
the closed position for attenuating propagation of a flame toward
the inlet, and wherein the fire retardant valve is operatively
associated with the flame detector such that detection of flame by
the flame detector causes the fire retardant valve to open allowing
the tire retardant to flow into the ducting system for attenuating
the detected flame; further comprising a supplementary gaseous feed
comprising a supplementary combustible component and a
supplementary gaseous feed valve for controlling flow of
supplementary gaseous feed into the flow of the gaseous feed
downstream of the shut-off valve, wherein the supplementary gaseous
feed is in fluid communication with a gas mixer for mixing the
gaseous feed with the supplementary gaseous feed.
2. A ducting system for conveying a flow of a gaseous feed of
ventilation air derived from a coal mine comprising a combustible
component from an inlet to at least one combustion module, the
system comprising: a sensor to measure a concentration of the
combustible component in the flow of the gaseous feed; a flame
detector; a shut-off valve configurable to have an open position to
allow the flow of the gaseous feed from the inlet to the at least
one combustion module and a closed position to prevent the flow of
the gaseous feed from the inlet to the at least one combustion
module; and a flame arrestor located in a flow path of the gaseous
feed upstream of the shut-oft valve, wherein the shut-off valve is
operatively associated with the sensor such that a measurement of a
concentration of the combustible component in flow of the gaseous
feed over a specified concentration by the sensor causes the
shut-off valve to be configured to the closed position for
preventing flow of a gaseous feed comprising a combustible mixture
of the combustible component from reaching an ignition source,
wherein the specified concentration is 1.25% methane as the
combustible component; and wherein the shut-off valve is
operatively associated with the flame detector such that detection
of flame by the flame detector causes the shut-off valve to be
configured to the closed position for attenuating propagation of a
flame toward the inlet; further comprising a supplementary gaseous
feed comprising a supplementary combustible component and a
supplementary gaseous feed valve for controlling flow of
supplementary gaseous feed into the flow of the gaseous feed
downstream of the shut-off valve, wherein the supplementary gaseous
feed is in fluid communication with a gas mixer for mixing the
gaseous feed with the supplementary gaseous feed.
3. The system according to claim 2, wherein the sensor is located
between the inlet and the shut-off valve at a position such that
the shut-off valve can be configured to the closed position prior
to a portion of the gaseous feed, comprising the combustible
component at a concentration over the specified concentration as
measured by the sensor, flowing to the shut-off valve.
4. The system according to claim 3, wherein the first sensor is
positioned proximal to a source of the gaseous feed.
5. The system according to claim 2, wherein the at least one
combustion module is shut down to remove the combustion module as a
potential ignition source upon measurement of a concentration of
the combustible component in the flow of the gaseous feed over the
specified concentration by the sensor and/or detection of flame by
the flame detector.
6. The system according to claim 2, further comprising a combustion
module flame arrestor located proximal each of the at least one
combustion modules.
7. The system according to claim 2 wherein the flame arrestor
comprises a crimped metal ribbon flame arrestor element.
8. The system according to claim 7, wherein the crimped metal
ribbon flame arrestor element has an expansion ratio greater than
1.
9. The system according to claim 7, wherein the crimped metal
ribbon flame arrestor element comprises a path length of from 10 mm
to 250 mm.
10. The system according to claim 2, further comprising a first
source of fresh air and a first fresh air valve for controlling
flow of the first source of fresh air into the ducting system,
wherein the first fresh air valve is operatively associated with
the shut-off valve such that when the shut-off valve is configured
to the closed position, the first fresh air valve is in an open
position to allow flow of fresh air into the system for diluting
the concentration of the combustible component.
11. The system according to claim 2, wherein at least one fire
retardant injection point is positioned upstream of the shut-off
valve and at least one fire retardant injection point is positioned
downstream of the shut-off valve.
12. The system according to claim 2, further comprising one or more
burst panels located upstream of the at least one combustion module
and downstream of at least one fire retardant injection point.
13. The system according to claim 2, further comprising a second
source of fresh air and a second fresh air valve for controlling
flow of the second source of fresh air into the flow of the gaseous
feed at a position upstream of the mixer.
14. The system according to claim 13, further comprising a pair of
supplementary sensors to measure a concentration of the combustible
component in the flow of the gaseous feed, wherein the pair
supplementary sensors comprise one supplementary sensor positioned
upstream of the mixer and another supplementary sensor positioned
downstream of the mixer and wherein the pair of supplementary
sensors are operatively associated with the second fresh air valve
and the supplementary gaseous feed valve for controlling the
concentration of the combustible component in the flow of the
gaseous feed leaving the mixer.
15. The system according to claim 2, further comprising a
ventilation air filter for filtering coal dust from the ventilation
air.
16. The system according to claim 15, wherein the ventilation air
filter is positioned upstream relative to the flame arrestor.
17. A ducting system for conveying a flow of a gaseous feed of
ventilation air derived from a coal mine comprising a combustible
component from an inlet to at least one combustion module, the
system comprising: a shut-off valve configurable to have an open
position to allow the flow of the gaseous feed from the inlet to
the at least one combustion module and a closed position to prevent
the flow of the gaseous feed from the inlet to the at least one
combustion module; a sensor to measure a concentration of the
combustible component in the flow of the gaseous feed, the sensor
located upstream of the shut-off valve; a flame detector located
downstream of the shut-off valve; a flame arrestor located in a
flow path of the gaseous feed upstream of the shut-off valve; a
source of fire retardant and a fire retardant valve feeding one or
more fire retardant injection points for controlling flow of the
fire retardant into the ducting system, the one or more fire
retardant injection points positioned between the flame arrestor
and the at least one combustion module; a supplementary gaseous
feed in fluid communication with a gas mixer for mixing the gaseous
feed with the supplementary gaseous feed, the supplementary gaseous
feed comprising a supplementary combustible component; a
supplementary gaseous feed valve for controlling flow of
supplementary gaseous feed into the flow of the gaseous feed
downstream of the shut-off valve; a source of fresh air and a fresh
air valve for controlling flow of the source of fresh air into the
flow of the gaseous feed at a position upstream of the mixer; and a
pair of supplementary sensors to measure a concentration of the
combustible component in the flow of the gaseous feed, wherein the
pair of supplementary sensors comprise one supplementary sensor
positioned upstream of the mixer and another supplementary sensor
positioned downstream of the mixer, wherein the shut-off valve is
operatively associated with the sensor such that a measurement of a
concentration of the combustible component in flow of the gaseous
feed over a specified concentration by the sensor causes the
shut-off valve to be configured to the closed position for
preventing flow of a gaseous feed comprising a combustible mixture
of the combustible component from reaching an ignition source,
wherein the specified concentration is 1.25% methane as the
combustible component, wherein the shut-off valve is operatively
associated with the flame detector such that detection of flame by
the flame detector causes the shut-off valve to be configured to
the closed position for attenuating propagation of a flame toward
the inlet, wherein the fire retardant valve is operatively
associated with the flame detector such that detection of flame by
the flame detector causes the fire retardant valve to open allowing
the fire retardant to flow into the ducting system for attenuating
the detected flame, and wherein the pair of supplementary sensors
are operatively associated with the second fresh air valve and the
supplementary gaseous feed valve for controlling the concentration
of the combustible component in the flow of the gaseous feed
leaving the mixer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority from Australian Provisional
Patent Application No 2015904458 filed on 30 Oct. 2015, the content
of which is incorporated herein by reference.
TECHNICAL FIELD
The present invention relates to a ducting system for a gaseous
feed comprising a combustible component, and more particularly for
a ducting system for conveying coal mine ventilation air comprising
methane to at least one combustion module.
BACKGROUND
It is often desirable to mitigate a component or components from a
fluid stream, particularly where the fluid stream is a gaseous
emission from a process which contains compounds which are harmful
to humans and/or the environment. Examples of such compounds
include volatile hydrocarbons such as methane (CH.sub.4). Fugitive
methane emissions occur from a variety of sources including coal,
oil and gas production, transport, mining, agriculture, waste
disposal, livestock, waste water treatment and land use
(forestry).
Current data indicates that, of the anthropogenic gases that
contribute to global warming, methane (CH.sub.4) is the most
significant after carbon dioxide (CO.sub.2). On a unit basis,
CH.sub.4 is estimated to be 25 times more potent at trapping heat
in the atmosphere than CO.sub.2 over a 100 year period. While
methane originates from several sources, fugitive CH.sub.4
emissions from coal mines represent approximately 8% of the world's
anthropogenic CH.sub.4, and contribute roughly 17% to anthropogenic
emissions. Coal mine methane (CMM) is not only a greenhouse gas but
also represents a significant wasted energy resource which, under
certain conditions, could be effectively used for electrical
generation, heating or chemical manufacturing feedstock. It was
estimated that about 28 billion m.sup.3 of CH.sub.4 (equivalent to
420 million tonnes of CO.sub.2) are emitted annually to the
atmosphere from coal mining activities around the world in
2010.
Depending on coal mine site specifications, approximately 50-85% of
all coal mining related methane is emitted to the atmosphere in
mine ventilation air. The development of technologies for
ventilation air methane (VAM) capture, mitigation and utilisation
are on-going challenges because the ventilation air volume flow
rate is large and the methane concentration is dilute and variable.
A typical gassy mine in Australia produces ventilation air at a
rate of approximately 120 to 600 m.sup.3/s with methane
concentrations of 0.3-1%.
Existing technologies used to mitigate methane from mine
ventilation air include a range of techniques such as techniques
based on methane oxidation and adsorption. In methane oxidation
systems, a gaseous feed containing methane is introduced to a
combustion module where the gaseous feed is heated. When the
gaseous feed reaches the auto-ignition temperature of methane,
oxidation of the methane takes place. The reaction can be
classified as either thermal oxidation occurring at temperatures in
the order of 850-1300.degree. C., or catalytic oxidation occurring
at temperatures in the order of 450-800.degree. C.
For mine site application, ventilation air is conveyed to VAM
combustion modules through a ducting system (either unenclosed or
enclosed) from the mine ventilation air shaft. Enclosed ducting is
required to capture the full ventilation air flow. Whether ducting
is unenclosed or enclosed, an unplanned event, e.g. the release of
a pocket of higher concentration methane into the ventilation air,
could result in an explosive mix of methane which is directly
ducted to a potential ignition source in the methane combustion
modules.
For combustion to occur, the level of a combustible gas must be
between its Lower Explosive Limit (LEL) and Upper Explosive Limit
(UEL). The upper and lower explosive limits are defined as the
lowest concentration (by percentage) of a gas or vapour in air that
is capable of producing a flash of fire in the presence of an
ignition source. For methane and air mixtures, the LEL is 5%
CH.sub.4 and the UEL is 15% CH.sub.4. In the event that a
combustible gas at levels in the LEL to UEL range comes into
contact with an ignition source, combustion may occur. In general,
there are two important regimes of combustion: deflagration and
detonation.
Deflagration is characterised by a subsonic flame front velocity.
The main mechanism of combustion propagation is of a flame that
propagates due to heat transfer effects. Detonation is
characterised by a supersonic flame front velocity which propagates
due to a powerful pressure wave that compresses the unburnt gas
ahead of the wave to a temperature above the auto-ignition
temperature. The effects of detonation on a confined system can be
devastating.
In confined systems such as ducting, obstacles in the flame path
such as elbows, sensors and other attachments can cause turbulence
in the flame, thus accelerating a subsonic flame (deflagration) to
a supersonic speeds (detonation). The transition from a
deflagration type of combustion to a detonation type of combustion
is known as the deflagration to detonation transition (DDT).
Due to the presence of combustible methane in ventilation air, when
any VAM technologies with a potential ignition source are
commercially implemented at mines, a major concern faced by the
coal industry is the safety of connecting the VAM combustion
modules to the mine ventilation air shaft. Existing ducting systems
for commercial scale VAM combustion modules operating at coal mines
rely on prevention methods utilising monitoring and mechanically
operated safety features. However, these existing prevention
measures can be unsuccessful as the failure of any one of the
monitoring and mechanically operated safety features can render the
entire fire prevention system useless. Furthermore, faulty
prevention measures can act as an ignition source in the system
which could result in the ignition of the combustible component
they were aimed at preventing.
Any discussion of documents, acts, materials, devices, articles or
the like which has been included in the present specification is
not to be taken as an admission that any or all of these matters
form part of the prior art base or were common general knowledge in
the field relevant to the present disclosure as it existed before
the priority date of each claim of this application.
SUMMARY
Throughout this specification the word "comprise", or variations
such as "comprises" or "comprising", will be understood to imply
the inclusion of a stated element, integer or step, or group of
elements, integers or steps, but not the exclusion of any element,
integer or step, or group of elements, integers or steps.
According to a first aspect of the present invention, there is
provided a ducting system for conveying a flow of a gaseous feed
comprising a combustible component from an inlet to at least one
combustion module, the system comprising:
a shut-off valve configurable to have an open position to allow the
flow of the gaseous feed from the inlet to the at least one
combustion module and a closed position to prevent the flow of the
gaseous feed from the inlet to the at least one combustion
module;
a sensor to measure a concentration of the combustible component in
the flow of the gaseous feed, the sensor located upstream of the
shut-off valve;
a flame detector located downstream of the shut-off valve;
a flame arrestor located in a flow path of the gaseous feed
upstream of the shut-off valve; and
a source of fire retardant and a fire retardant valve feeding one
or more fire retardant injection points for controlling flow of the
fire retardant into the ducting system, the one or more fire
retardant injection points positioned between the flame arrestor
and the at least one combustion module,
wherein the shut-off valve is operatively associated with the
sensor such that a measurement of a concentration of the
combustible component in the gaseous feed over a specified
concentration by the one sensor causes the shut-off valve to be
configured to the closed position for preventing flow of a gaseous
feed comprising a combustible mixture of the combustible component
from reaching an ignition source,
wherein the shut-off valve is operatively associated with the flame
detector such that detection of flame by the flame detector causes
the shut-off valve to be configured to the closed position for
attenuating propagation of a flame toward the inlet, and
wherein the fire retardant valve is operatively associated with the
flame detector such that detection of flame by the flame detector
causes the fire retardant valve to open allowing the fire retardant
to flow into the ducting system for attenuating the detected
flame.
As ancillary equipment such as the shut-off valve, when faulty, may
act as an ignition source, the flame arrestor is located upstream
of any potential ignition sources. However, as this may be located
some distance from the combustion modules, another potential source
of ignition, the likelihood of a flame originating at the
combustion modules has an increased likelihood of undergoing DDT.
This likelihood further increases with the presence of turbulence
inducing features along the ducting. As such, the flame arrestor
positioned upstream of the shut-off valve may be a detonation rated
flame arrestor.
The flame arrestor in the flow path of the gaseous feed upstream of
the shut-off valve may act to attenuate propagation of a flame
between a source of ignition, such as the combustion modules, and
the inlet should any one of the fire prevention measures fail and
ignition of the gaseous feed were to occur. The shut-off valve in
combination with the sensor may act to prevent combustion of the
gaseous feed occurring by preventing a portion of the feed
containing a combustible mixture of the combustible component from
reaching potential ignition sources such as the combustion modules.
In addition, the shut-off valve in combination with the flame
detector may act to attenuate combustion by providing a barrier to
a flame front propagating toward the inlet.
The fire retardant injection points are preferably positioned
between the flame arrestor and the one or more combustion modules.
While flame arrestors are typically positioned in close proximity
to potential sources of ignition, the addition of the fire
retardant injection points downstream of the flame arrestors have
been found to advantageously inhibit the severity of the flame
propagation front, thereby enabling a lower rated flame arrestor to
be used or further enhancing the flame arresting. Indeed, the
strategy of multiple flame prevention measures in co-operation with
multiple flame attenuation measures enables the required safety
requirements to be met without having to rely upon a few highly
rated protection devices, which may be difficult to replace or
repair, with the consequence of device failure often
catastrophic.
Preferably, the sensor is located between the inlet and the
shut-off valve at a position such that the shut-off valve can be
configured to the closed position prior to a portion of the gaseous
feed, comprising the combustible component at a concentration over
the specified concentration as measured by the first sensor,
flowing to the shut-off valve. It will be appreciated that the
further the sensor is positioned from the shut-off valve, the more
time there is for the shut-off valve to operate prior to the
portion of the gaseous feed flowing from the sensor to the shut-off
valve. Preferably the sensor positioned at least 50 m, more
preferably 100 m, upstream of the shut-off valve. Most preferably,
the sensor is positioned at the furthest available distance from
the shut-off valve, for example adjacent the source of the gaseous
feed. The further the distance between the sensor and the shut-off
valve the greater time the sensor has to activate the flame
retardant mechanisms downstream to avoid or lessen the impact of
potential fire or explosion and resultant flash or burn back.
The at least one combustion module is preferably shut down to
remove the combustion module as a potential ignition source upon
measurement of a concentration of the combustible component in the
flow of the gaseous feed over the specified concentration by the at
least one sensor and/or detection of flame by the flame
detector.
The ducting system may be for use with a plurality of combustion
modules, the system further comprising a plurality of combustion
module pipes, wherein each combustion module is in fluid
communication with a respective combustion module pipe. Preferably,
each combustion module pipe comprises a combustion module inlet
valve and a flame detector positioned between the combustion module
and the combustion module inlet valve.
Each combustion module pipe may comprise:
the flame detector;
the shut-off valve; and
the flame arrestor located upstream of the shut-off valve.
Each combustion module pipe may comprise a supplementary sensor to
measure a concentration of the combustible component in the flow of
the gaseous feed, wherein a combustion module may be shut down upon
measurement of a concentration of the combustible component in the
flow of the gaseous feed over the specified concentration and/or
detection of flame at the respective combustion module pipe.
As the combustion modules present a potential ignition source, a
combustion module flame arrestor is preferably positioned proximal
to each of the at least one combustion modules. By positioning a
combustion module flame arrestor close to the ignition source can
minimise the potential distance of travel of a flame originating at
the combustion module which decreases the likelihood of the flame
undergoing a deflagration to detonation transition (DDT). As such,
the combustion module flame arrestors positioned proximal to the
combustion modules may be a deflagration rated flame arrestor.
The flame arrestor may be any suitable flame arrestor, for example
the flame arrestor may be selected from crimped metal ribbon,
parallel plate, expanded metal cartridge, perforated plate, wire
gauze, sintered metal, metal shot, ceramic balls and/or compressed
wire wool flame arrestor elements.
In certain embodiments, the flame arrestor comprises a crimped
metal ribbon flame arrestor element. The flame arrestor may also
comprise two or more crimped metal ribbon flame arrestor elements
in series or in parallel.
It will be appreciated that the dimensions and characteristics of
the crimped metal ribbon flame arrestor elements may be selected
based on a number of factors such as pipe diameter, gas flow rate
and gas composition. Further considerations may include the
position of the flame arrestor relative to potential ignition
sources, and the types, quantity and position of flame attenuation
measures positioned between potential ignitions sources and the
flame arrestor. The inventors have found that the configurations of
flame attenuation measures described in the present invention to be
particularly effective when working in co-operation with the flame
arrestor, such that there is greater design freedom in the type,
size and positioning of the flame arrestor.
Preferably, the crimped metal ribbon flame arrestor element has an
expansion ratio greater than about 1, preferably from about 1 to
about 5, and more preferably about 2. The crimped metal ribbon
flame arrestor element path length may be of any suitable length,
preferably from about 10 mm to about 250 mm. Optionally, the at
least one crimped metal ribbon flame arrestor element comprises at
least one support member 231 extending radially through the crimped
metal ribbon flame arrestor element.
The system may further comprise a first source of fresh air and a
first fresh air valve for controlling flow of the first source of
fresh air into the system. The first fresh air valve may be
operatively associated with the shut-off valve such that when the
shut-off valve is configured to the closed position, the first
fresh air valve is in an open position to allow flow of fresh air
into the system for diluting the concentration of the combustible
component.
The one or more fire retardant injection points preferably define a
fire retardant injection zone in the ducting system. The fire
retardant injection zone is preferably from 1 to 100 m in length,
more preferably the injection zone is from 5 to 50 m in length. The
fire retardant may be any suitable fire retardant for attenuating
flame. For example the fire retardant may be a fluid, e.g. a liquid
such as water or a gas such as an inert gas. In a preferred form,
the fire retardant is carbon dioxide. Preferably, at least one fire
retardant injection point is positioned upstream of the shut-off
valve and at least one fire retardant injection point is positioned
downstream of the shut-off valve.
Preferably, the system further comprises one or more burst panels
located upstream of the at least one combustion module. More
preferably, the one or more burst panels are used in co-operation
with the one or more fire retardant injection points. In such
embodiments, the one or more burst panels are preferably positioned
downstream of the fire retardant injection points. In this
configuration, activation of the flame detector causes the flame
retardant to be injected into the duct, thereby increasing the duct
pressure and activation the burst panel earlier than if the flame
retardant was not injected into the duct. Furthermore, positioning
of the burst panels downstream of the flame arrestor enables that
the activation of the burst panel prevents damage to upstream
devices.
The system may further comprise a supplementary gaseous feed
comprising a supplementary combustible component and a
supplementary gaseous feed valve for controlling flow of
supplementary gaseous feed into the flow of the gaseous feed
downstream of the shut-off valve. The supplementary gaseous feed is
preferably in fluid communication with a gas mixer for mixing the
gaseous feed with the supplementary gaseous feed whereby the
supplementary gaseous feed is fluidly connected to the mixer by a
supplementary gaseous feed pipe, the pipe comprising one or more
of: the supplementary gaseous feed valve, a fuel filter, a fuel
flame arrestor, a fuel check valve, a fuel pressure regulator
and/or one or more fuel valves. The system may further comprise a
supplementary gaseous feed flow monitor and controller.
The system may further comprise a second source of fresh air and a
second fresh air valve for controlling flow of the second source of
fresh air into the flow of the gaseous feed at a position upstream
of the mixer. Preferably, the system further comprises a pair of
supplementary sensors to measure a concentration of the combustible
component in the flow of the gaseous feed, wherein the
supplementary sensors are positioned upstream and downstream of the
mixer, respectively, and wherein the supplementary sensors are
operatively associated with the second fresh air valve and the
supplementary gaseous feed valve for controlling the concentration
of the combustible component in the flow of the gaseous feed
leaving the mixer.
The gaseous feed may be ventilation air derived from a coal mine
and the volatile component is methane. Where methane is the
combustible gas, the specified concentration is preferably below
the lower explosive limit for methane, and more preferably the
specified concentration is 1.25%. Preferably, the system further
comprises a ventilation air filter for filtering coal dust from the
ventilation air. The ventilation air filter is preferably
positioned upstream relative to the flame arrestor.
According to a second aspect of the present invention, there is
provided a ducting system for conveying a flow of a gaseous feed
comprising a combustible component from an inlet to at least one
combustion module, the system comprising:
a sensor for measuring a concentration of the combustible component
in the flow of the gaseous feed;
a flame detector;
a shut-off valve configurable to have an open position to allow the
flow of the gaseous feed from the inlet to the at least one
combustion module and a closed position to prevent the flow of the
gaseous feed from the inlet to the at least one combustion module;
and
a flame arrestor located in a flow path of the gaseous feed
upstream of the shut-off valve,
wherein the shut-off valve is operatively associated with the
sensor such that a measurement of a concentration of the
combustible component in the gaseous feed over a specified
concentration by the one sensor causes the shut-off valve to be
configured to the closed position for preventing flow of a gaseous
feed comprising a combustible mixture of the combustible component
from reaching an ignition source; and
wherein the shut-off valve is operatively associated with the flame
detector such that detection of flame by the flame detector causes
the shut-off valve to be configured to the closed position for
attenuating propagation of a flame toward the inlet.
According to a third aspect of the present invention, there is
provided a ducting system for conveying a flow of a gaseous feed
comprising a combustible component from an inlet to at least one
combustion module, the system comprising:
a shut-off valve configurable to have an open position to allow the
flow of the gaseous feed from the inlet to the at least one
combustion module and a closed position to prevent the flow of the
gaseous feed from the inlet to the at least one combustion
module;
a sensor to measure a concentration of the combustible component in
the flow of the gaseous feed, the sensor located upstream of the
shut-off valve;
a flame detector located downstream of the shut-off valve;
a flame arrestor located in a flow path of the gaseous feed
upstream of the shut-off valve;
a source of fire retardant and a fire retardant valve feeding one
or more fire retardant injection points for controlling flow of the
fire retardant into the ducting system, the one or more fire
retardant injection points positioned between the flame arrestor
and the at least one combustion module;
a supplementary gaseous feed in fluid communication with a gas
mixer for mixing the gaseous feed with the supplementary gaseous
feed, the supplementary gaseous feed comprising a supplementary
combustible component;
a supplementary gaseous feed valve for controlling flow of
supplementary gaseous feed into the flow of the gaseous feed
downstream of the shut-off valve;
a source of fresh air and a fresh air valve for controlling flow of
the source of fresh air into the flow of the gaseous feed at a
position upstream of the mixer; and
a pair of supplementary sensors to measure a concentration of the
combustible component in the flow of the gaseous feed, the
supplementary sensors positioned upstream and downstream of the
mixer, respectively,
wherein the shut-off valve is operatively associated with the
sensor such that a measurement of a concentration of the
combustible component in flow of the gaseous feed over a specified
concentration by the sensor causes the shut-off valve to be
configured to the closed position for preventing flow of a gaseous
feed comprising a combustible mixture of the combustible component
from reaching an ignition source,
wherein the shut-off valve is operatively associated with the flame
detector such that detection of flame by the flame detector causes
the shut-off valve to be configured to the closed position for
attenuating propagation of a flame toward the inlet,
wherein the fire retardant valve is operatively associated with the
flame detector such that detection of flame by the flame detector
causes the fire retardant valve to open allowing the fire retardant
to flow into the ducting system for attenuating the detected flame,
and
wherein the supplementary sensors are operatively associated with
the second fresh air valve and the supplementary gaseous feed valve
for controlling the concentration of the combustible component in
the flow of the gaseous feed leaving the mixer.
It will be appreciated that additional features described for the
first aspect above may also form additional features of this second
and third aspects where appropriate.
According to a fourth aspect, there is provided a system for
mitigating methane from coal mine ventilation air comprising:
a ducting system according to any one of the first, second or third
aspects; and
a plurality of combustion modules in fluid communication with the
ducting system.
In some embodiments, the combustion modules may include a body
portion formed from a refractory material and having a plurality of
bores extending therethrough, the bores facilitating the flow of
the gaseous feed through the body portion and transfer of heat to
the gaseous feed.
Preferably, the bores are substantially parallel to one another and
have a width of from about 1 mm to about 10 mm, are spaced apart a
distance of from about 2 mm to about 25 mm from the centre points
of the bores, and the body portion has a height, width and depth
each from about 1 m to about 3 m.
The refractory material may be selected from a ceramic material,
alumina, silica, magnesia, lime, fireclays, zirconia, dolomite,
mullite, castable refractory cement and mixtures thereof.
The body portion may be heated to a temperature of from about
900.degree. C. to about 1200.degree. C.
Alternatively, the body portion may include at least one catalyst
disposed on internal wall of the bores, or disposed in the
refractory material, and the body portion may then only be required
to be heated to a temperature of from about 200.degree. C. to about
700.degree. C.
In other embodiments, the combustion modules may include a body
portion in the form of a honeycomb-type monolith catalytic
combustor. The catalytic combustor may contain any suitable
catalyst for the system, for example a catalyst having an activity
of 50.times.10.sup.-7 to 200.times.10.sup.-7 mole/m.sup.2s and a
reaction surface area of 20 to 40 m.sup.2/cm.sup.2. The
honeycomb-type monolith catalytic combustor may comprise a ceramic
monolith which acts as a substrate for a wash coat slurry of base
metals on which a noble metal catalyst is placed.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the present invention will now be described, by way
of example only, with reference to the accompanying drawings, in
which:
FIG. 1 is a schematic diagram of a first configuration of a ducting
system according to the invention;
FIG. 2 is a schematic diagram of a second configuration of a
ducting system according to the invention;
FIG. 3 is a schematic diagram of a third configuration of a ducting
system according to the invention;
FIG. 4 is a schematic diagram of a fourth configuration of a
ducting system according to the invention;
FIG. 5 is a schematic diagram of a crimped metal ribbon flame
arrestor;
FIG. 6 is a side view of a channel of the flame arrestor of FIG. 5;
and
FIG. 7 is a body portion ventilation air methane (VAM) combustion
module.
DESCRIPTION OF EMBODIMENTS
Referring initially to FIGS. 1 to 4, where like features have been
given like numbers, there is provided a number of configurations of
a ducting system 100 for conveying flow of a gaseous feed 110 such
as coal mine ventilation air having a combustible component in the
form of methane. The ducting system 100 allows a flow of gaseous
feed 110 from an inlet (not shown) to a plurality of combustion
modules 12.
As used herein, upstream refers to a position situated in the
opposite direction to the direction of flow of the gaseous feed
(i.e. towards the inlet) and downstream refers to a position
situated in the same direction as the direction of flow of the
gaseous feed (i.e. towards the combustion modules 12).
In each configuration, the ventilation air 110 flows from the inlet
(not shown), through the ventilation air shaft 1 and past a sensor
C0 for measuring a concentration of methane in the ventilation air.
A shut-off valve 6 is operatively associated with the sensor C0
such that a measurement of methane above a specified concentration
by the sensor C0 causes the shut-off valve 6 to be configured to a
closed position preventing further flow of the gaseous feed 110
toward potential ignition sources such as the combustion modules
12.
As shown in FIGS. 1 to 4, the sensor C0 is positioned upstream of
the shut-off valve 6. It is preferred that the first sensor C0 is
positioned as far underground as possible, i.e. as close to the
source of the ventilation air as possible. By locating the first
sensor C0 as far from the shut-off valve 6 as possible, the earlier
a pocket of gas containing a potentially combustible concentration
of methane entering the system 100 can be detected and preventative
measures such as closing shut-off valve 6 and shutting down the
combustion units 12 can be implemented.
A pair of supplementary sensors C1 and C2 for measuring the
concentration of methane in the flow of the ventilation air are
also provided. In addition to monitoring for potentially
combustible concentrations of methane, which also triggers the
closure of shut-off valve 6 and shut down of the combustion modules
12 as described in relation to the sensor C0 above, the
supplementary sensors C1 and C2 assist in maintaining the
concentration of methane in preferred operational limits for
mitigation by the combustion units 12.
The supplementary sensors C1 and C2 are positioned upstream and
downstream, respectively, of a mixer 8. A supplementary gaseous
feed 140 comprising methane is provided in fluid communication with
the mixer 8. The supplementary sensors C1 and C2 are operatively
associated with a fresh air valve 7 and a supplementary gaseous
feed valve 13 for controlling the concentration of the methane in
the flow of the ventilation air leaving the mixer 8.
The combination of the sensors C0, C1, C2 and the shut off valve 6
aim to prevent fire occurring by maintaining the concentration of
methane below its lower explosive limit and, where a measurement of
the concentration of methane above a specified value is detected,
preventing flow of the ventilation air comprising a potentially
combustible mixture of methane from flowing towards potential
ignition sources such as the combustion modules 12. However, in the
event that the preventative measures should fail, the ducting
system 100 is further provided with measures, as described below,
for attenuating a flame should ignition of the ventilation air
occur.
Flame detectors F0, F1, F2, F3, . . . , Fn are provided downstream
of the shut-off valve 6. The flame detectors F0, F1, F2, F3, . . .
, Fn are shown positioned adjacent each combustion unit 12, however
it will be appreciated that additional flame detectors F0, F1, F2,
F3, . . . , Fn may be positioned adjacent any ancillary equipment
that may present as a potential ignition source. The shut-off valve
6 is operatively associated with the flame detectors F0, F1, F2,
F3, . . . , Fn such that detection of a flame by any one of the
flame detectors F0, F1, F2, F3, . . . , Fn to be configured to a
closed position thereby providing a barrier to the flame from
propagating toward the inlet.
A source of fire retardant 11 and a fire retardant valve 10 for
controlling the flow of fire retardant into the system may also be
provided. The fire retardant valve 10 is operatively associated
with the flame detectors F0, F1, F2, F3, . . . , Fn such that
detection of flame by the flame detector F0, F1, F2, F3, . . . , Fn
causes the fire retardant valve 10 to open allowing fire retardant
to flow into the ducting system at one or more fire retardant
injection points defining a fire injection zone for attenuating the
detected flame. For example, the fire retardant is configured to
flow into the system at fire retardant injection points on both
sides of the shut-off valve 6 such that, as the detection of the
flame by the flame detectors F0, F1, F2, F3, . . . , Fn causes the
shut-off valve 6 to close, the fire retardant would be prevented
from flowing to sections on either side of the shut-off valve 6.
Furthermore, the fire retardant is preferably configured to flow
into the ducting system 100 at fire retardant injection points
upstream of potential ignition sources to provide additional time
from the detection of a flame for the fire retardant to flow into
the ducting system 100.
Burst panels 23 are further provided between the fire retardant
injection points and the combustion modules for releasing the
pressure inside the ducting in the event of fire or an explosion.
In the event of a flame detection by the flame detectors F0, F1,
F2, F3, . . . , Fn, shut-off valve 6 closes and fire retardant
valve 10 opens allowing fire retardant to flow into the ducting
system downstream of the shut-off valve. The introduction of fire
retardant and closure of the shut-off valve may lead to an increase
in pressure in the portion of the ducting downstream of the
shut-off valve. This increase in pressure may be as a result of the
flame propagation, the introduction of pressurised fire retardant
and the reaction between the flame and the fire retardant (e.g.
heating of a gas fire retardant or vapourisation of a liquid fire
retardant such as water). This increase in pressure leads to a
bursting of the burst panels 23 which protects this portion of the
duct from deformation and provides a low pressure path for the
flame to be directed outside of the ducting system 100.
A flame arrestor 5, described in more detail below, is further
provided upstream of any potential ignition sources including the
shut-off valve 6. Any flame that progresses through the above
described flame attenuation measures comes into contact with the
flame arrestor for further attenuation. It will be appreciated
that, in the event that the above measures fail to quench the flame
entirely, the flame will be greatly attenuated relative to a system
not including such measures.
As the combustion modules 12 present a potential ignition source,
additional flame arrestors may be provided in close proximity to
the combustion modules 12, for example between the combustion
module 12 and the combustion module inlet valve 22. Positioning a
flame arrestor close to an ignition source can minimise the
potential distance of travel of a flame originating at the
combustion module 12 which decreases the likelihood of the flame
undergoing a deflagration to detonation transition (DDT). As such,
any flame arrestor positioned between the combustion module 12 and
the combustion module inlet valve 22 may be a deflagration rated
flame arrestor. The presence of a flame arrestor in proximity to
the combustion modules may also reduce the physical requirements of
the flame arrestor 5 positioned upstream of the shut-off valve
6.
Specific configurations of the ducting system 100 will now be
described with reference to FIGS. 1 to 4.
Configuration 1
Referring to FIG. 1, a fully enclosed ducting system 100 is
provided comprising a ventilation air fan 2 for conveying the flow
of coal mine ventilation air 110 containing the combustible
component methane from the ventilation air shaft 1 through a main
duct 120 to a plurality of ventilation air methane (VAM) combustion
modules 12, where each VAM combustion module 12 is fluidly
connected to the main duct via a respective combustion module pipe
130.
From the ventilation air shaft 1, the coal mine ventilation air 110
passes through a ventilation air filter 4 for filtering coal dust
from the ventilation air and a flame arrestor 5. The flame arrestor
5 may be any suitable flame arrestor, for example a crimped metal
ribbon flame arrestor 300 of the type shown in FIGS. 5 and 6 and as
discussed in more detail below. By locating the flame arrestor 5 in
a flow path of the coal mine ventilation air 110, this may
attenuate propagation of a flame between the combustion module 12
and the inlet. This may be advantageous should other fire
prevention measures fail and ignition of the coal mine ventilation
air 110 in the system 100 were to occur.
A three-way butterfly valve 6 is provided such that, when operated,
simultaneously stops the flow of ventilation air 110 toward the VAM
combustion modules 12 and opens a valve to allow a flow of fresh
air into the system thereby to dilute the concentration of methane
in the flow of the ventilation air 110. The three-way butterfly
valve 6 is operated in the event of the detection of a
concentration of methane above a specified value by any one of the
methane sensors C0, C1, C2 located throughout the ducting system,
or the detection of flame by any one of the number of flame
detectors F0, F1, F2, F3, . . . , Fn. The three-way butterfly valve
6 may be automatically operated after receiving a control signal
from a controller (not shown), which may provide the control signal
in response to sensor signals from methane sensors C0, C1, C2 and
flame detectors F0, F1, F2, F3, . . . , Fn.
An additional fresh air supply is provided, with the flow of fresh
air into the flow of ventilation air controlled by fresh air valve
7. During standard operation, when the methane concentration is
required to be brought down by operational requirements of the
downstream VAM combustion modules 12, the fresh air is sucked into
the ventilation air by controlling the fresh air valve 7. The fresh
air flow rate is controlled by the methane sensors C1 and C2. C1 is
used to monitor the methane concentration in the ventilation air,
and C2 for the methane concentration after the valve 7, i.e. the
methane concentration in the flow of ventilation air 110 being
conveyed to the VAM combustion modules 12.
When the methane concentration is required to be brought up to a
certain level for the self-sustaining operation of the downstream
VAM combustion modules, a supplementary gaseous feed 140 such as
coal mine drainage gas is injected into the flow of ventilation air
110 through mixer 8. The supplementary gaseous feed 140 is supplied
from a source through a supplementary gaseous feed pipe 150
comprising a supplementary gaseous feed valve 13, fuel filter 14,
fuel flame arrestor 15, fuel check valve 16, fuel pressure
regulator 17 and fuel valves 18. The flow rate of the supplementary
gaseous feed 140 is monitored and controlled via a fuel flow
monitor and controller 19. The supplementary gaseous feed 140 flow
rate is determined by methane sensors C1 and C2. C1 is used to
monitor the methane concentration in the flow of ventilation air
upstream of mixer 8, and C2 for the methane concentration
downstream of mixer 8, i.e. the methane concentration in the flow
of ventilation air 110 being conveyed to the VAM combustion
modules. The mixer 8 can be any type of mixer for mixing the
supplementary gaseous feed 140 and flow of ventilation air 110,
e.g. an array of fuel nozzles around the ventilation air
ducting.
In the event of a methane reading by any one of the methane sensors
C0, C1, C2 above the specified value, for example a value of 1.25%,
the valve 6 will be operated to be closed to the flow of
ventilation air 110 and open to the fresh air supply. In addition,
the two fuel valves 18 will also be operated to close to ensure no
additional methane is being introduced to the system, and the VAM
combustion modules 12 are shut down. Valves 6, 18 and the VAM
combustion modules 12 will be similarly operated in the event of
any one of the flame detectors F0, F1, F2, F3, . . . , Fn detecting
a flame.
In addition to the flame prevention measures discussed above, the
ducting system also provides a number of measures for suppressing
flame propagation should fire occur. One measure includes the
provision of a flame arrestor 5, discussed in more detail below, in
the flow path from the ventilation shaft 1 to the VAM combustion
modules and an additional flame arrestor 15 in the supplementary
gaseous feed pipe 150. In addition, a source of inert gas 11, for
example compressed CO.sub.2, is also provided with flow of CO.sub.2
into the ducting system 100 controlled by inert gas valve 11. The
inert gas valve 11 is configured to open in the event of a flame
being detected by any one of the flame detectors F0, F1, F2, F3, .
. . , Fn such that CO.sub.2 flows into the main duct at various
positions through an array of nozzles.
To avoid ventilation air fan 2 back pressure and shaft exit
blockage when the ducting system is not operated correctly or in
the case of emergency where the three-way butterfly valve 6 is
closed to the flow of ventilation air 110, two gravity-based
hanging doors 3 (one per side) can be used. The hanging doors 3 can
be pushed open automatically by ventilation air pressure. When the
ducting is in normal operation, and a pressure balance is achieved
by the extraction fan 9, the hanging doors 3 are in a closed
position. The selection of the cross-sectional area of the hanging
doors 3 is dependent on the ventilation air flow rate and
pressure.
One or more burst panels 23 are installed downstream of the mixer 8
to release the pressure inside the ducting if the explosion occurs.
The burst panels 23 can be rated to 50 kPa or 100 kPa or other
valve, and the use of burst panels 23 can reduce the required duct
wall thickness. The size of the burst panels 23 is determined based
on the duct size and gas flow rate in the duct.
A drainage valve 21 is also provided for draining any condensed
water inside the ducting.
Configuration 2
A second configuration of a ducting system is shown in FIG. 2.
Configuration 2 is a similar set up to configuration 1 however some
of the components of the ducting system of FIG. 1 are provided in
each individual combustion module pipe 130 leading to the VAM
combustion modules 12. In this way, if there is a high methane
reading at sensors C0, C1, C2 in one of the combustion module pipes
130, or flame detected at flame detector F1 in one of the
combustion module pipes, only the affected pipe will be shut down
and the remaining VAM combustion modules 12 on unaffected pipes can
continue to operate. This configuration also allows flexibility in
whether some or all the VAM combustion modules 12 are provided with
fuel mixing to control the methane concentration. Furthermore, with
a ducting system 100 of this configuration, the maintenance,
replacement or other work being conducted on components of the
ducting system may only require the VAM combustion module 12 on the
affected combustion module pipe to be shut down, allowing the other
VAM combustion modules on the remaining combustion module pipes to
continue to operate.
Configuration 3
Configuration 3 is the same as configuration 1 applied to an
unenclosed ducting system 100 whereby a ventilation air hood 20 is
used to collect ventilation air 110 from above a ventilation air
shaft outlet 160.
Configuration 4
Configuration 4 is the same as configuration 2 applied to an
unenclosed ducting system 100 whereby a ventilation air hood 20 is
used to collect ventilation air 110 from above a ventilation air
shaft outlet 160.
Flame Arrestors
Flame arrestors are designed to allow the flow of gas therethrough
while preventing the propagation of a flame front by removal of
heat from the flame as it passes through the flame arrestor. In
general, there are two important regimes of explosion: deflagration
and detonation. Deflagration normally propagates at a velocity
below the speed of sound and the maximum pressure is 0.7 MPa.
Detonation waves proceed at supersonic velocities, ranging from
1,000 m/s to 2,500 m/s with a maximum pressure up to 1.7 MPa and
can cause extreme destruction that is much harder to arrest than
deflagration. It is therefore very important to determine whether
and how deflagration or detonation can occur for various geometries
and mixture compositions of ventilation air ducting so that optimum
safety requirements can be designed into the ventilation air
ducting system.
In the above described ducting systems, flame arrestors 5 are
positioned between the combustion modules 12 and the ventilation
air shaft 1 to suppress the flame propagation back to the mine in
the event that ignition of the flow of gaseous feed were to occur.
Additional flame arrestors 15 are provided in the supplementary
gaseous feed pipe. It will be appreciated that further flame
arrestors may also be provided adjacent potential ignition sources
to at least partially quench a flame should ignition occur and
therefore reduce the load on the final flame arrestor 5. For
example, combustion module flame arrestors may be positioned
proximal to the combustion modules 12. Selection of a flame
arrestor rated for deflagration and/or detonation depend on how the
ducting is designed for its practical application, such as its
length, diameter, shape, bends and equipment. It is important to
design the ducting in a manner to minimise the likelihood of a
deflagration to detonation transition (DDT) should a fire occur,
for example by minimising features in the ducting that could
increase turbulence of a flame, such as elbows, sensors and other
attachments.
There are many types of flame arrestors. A flame arrestor for use
in the safe ducting system may comprise crimped metal ribbon,
parallel plate, expanded metal cartridge, perforated plate, wire
gauze, sintered metal, metal shot, ceramic balls and/or compressed
wire wool flame arrestor elements.
Referring to FIGS. 5 and 6, crimped metal ribbon flame arrestor
elements 200 are characterised by alternating layers of crimped
metal ribbons 210 and flat metal ribbons 220 which are wound
together to form a layered cylinder. The spaces between the crimped
and flat ribbons provide multiple small channels 230 of
approximately triangular cross-section.
Crimped metal ribbon flame arrestor elements can be characterised
by a number of parameters, including ribbon thickness, element
thickness b and element diameter D. The channels formed in the
spaces between the corrugations and the flat ribbon can be
characterised by the height h and bottom side width a of the
triangle, as shown in FIG. 6. The path length L is defined by the
element inclination a and the element thickness b, i.e. L=b/a. The
expansion ratio .beta. is defined as the ratio of the element
diameter D to the pipe diameter d, i.e. .beta.=D/d.
The design of a crimped metal ribbon flame arrestor element
suitable for use in ducting between a coal mine ventilation air
shaft and VAM combustion modules must take into account various
features specific to the system such as flow rate of the
ventilation air through the ducting, composition, dust content and
pipe size.
For example, it has been found that channels of smaller
cross-sectional area increases flame quenching efficiency, however
smaller channels are more prone to fouling with coal dust which can
lead to increased requirement for cleaning and replacement of the
arrestor, potential failure of quenching and increased ventilation
air flow resistance. Similarly, increased channel length L has been
found to increase flame quenching efficiency, while also increasing
the flow resistance. The crimped metal ribbon flame arrestor path
length L may be of any suitable length, preferably from about 10 mm
to about 250 mm. It will be appreciated that the path length for a
system can be increased by providing two or more crimped metal
ribbon arrestor elements in series.
The expansion ratio (3, the ratio of the element diameter D to pipe
diameter d, can also be an important parameter. It has been found
that increasing the expansion ratio, i.e. increasing the element
diameter D increases the flame quenching efficiency. However, pipes
used in conveying coal mine ventilation air are significantly
larger than pipes for which flame arrestors are currently designed
for. For example, the main duct 110 for conveying coal mine
ventilation air 110 may be in the order of about 5 m in diameter.
Combustion module pipes are generally significantly smaller in
diameter than the main duct, for example the combustion module
pipes may be around 1 m in diameter.
Preferably, the flame arrestor has an expansion ratio .beta.
greater than about 1, preferably from about 1 to about 5, and more
preferably about 2. However, increasing the element diameter D can
lead to increased risk of damage during handling, installation and
use with the potential for enlarged or collapsed channels which can
decrease the flame quenching efficiency and increase flow
resistance. To increase durability, support members may be
introduced to the flame arrestor, such as metal rods, extending
radially through the cylinder of the flame arrestor. Furthermore,
two or more crimped metal ribbon flame arrestor elements can be
provided in parallel to provide process higher ventilation air flow
rates without needing to increase the diameter of the flame
arrestor elements.
VAM Combustion Modules
Suitable VAM combustion modules include the system for mitigating a
volatile component from a gaseous feed as described in AU
2009338680 and the system for catalytic combustion as described in
U.S. Pat. No. 7,430,869, both of which are incorporated herein by
reference.
In certain embodiments, VAM mitigation combustion modules 12 of the
type described in AU 2009338680, which is incorporated herein by
reference, are used. Referring to FIG. 7, the body portion 300 of
the VAM mitigation combustion module 12 includes an array of bores
310 that extend through the body portion 300 from a first end to an
opposing second end. The bores 310 have a circular cross section
with a diameter of 3 mm and are spaced apart at distance of
approximately 4 mm taken from the centre points of the bores. The
body portion is substantially cube-shaped, having a height, width
and depth each of from about 1 m to about 3 m.
During start-up of the combustion module, the body portion is
heated to a desired temperature, generally about 1200.degree. C.
Inclusion of a catalyst in the body portion, for example within the
material of the body portion itself or applied to the walls of the
bores extending therethrough, may dictate a relatively low start up
temperature of from about 200.degree. C. to about 700.degree.
C.
The ventilation air containing methane flows through the bores of
the body portion. The ventilation air is initially at a temperature
of about 25.degree. C. (i.e. ambient temperature) and increases in
temperature as it passes through the combustion module by absorbing
heat from the inner walls of the bores until it reaches
auto-ignition temperature of the methane. At this point, oxidation
takes place resulting in relatively high temperature gaseous
emission that provides heat to the body portion as it exits the
combustion module. The direction of ventilation air flow through
the body portion may be periodically reversed between a forward
flow 320 and a reverse flow 330 to utilise the heat generated by
the combustion process and therefore reduce the energy consumption
of the combustion module 12.
In other embodiments, VAM catalytic combustion modules 12 of the
type described in U.S. Pat. No. 7,430,869, which is incorporated
herein by reference, may be used. VAM catalytic combustion modules
12 may include a body portion in the form of a honeycomb-type
monolith catalytic combustor. The catalytic combustor may contain
any suitable catalyst for the system, for example a catalyst having
an activity of 50.times.10.sup.-7 to 200.times.10.sup.-7
mole/m.sup.2s and a reaction surface area of 20 to 40
m.sup.2/cm.sup.2. The honeycomb-type monolith catalytic combustor
may comprise a ceramic monolith which acts as a substrate for a
wash coat slurry of base metals on which a noble metal catalyst is
placed.
It will be appreciated by persons skilled in the art that numerous
variations and/or modifications may be made to the above-described
embodiments, without departing from the broad general scope of the
present disclosure. The present embodiments are, therefore, to be
considered in all respects as illustrative and not restrictive.
* * * * *